Introduction of short strands of antisense DNA with sequences complementary to the mRNA encoding a particular protein inside the cell is being explored as a therapeutic approach[1]. The inserted antisense oligonucleotide (“ODN”) binds specifically and strongly to its mRNA target through Watson-Crick base pairing and blocks gene expression either through translational inhibition or enzymatic cleavage of the mRNA target [2]. Antisense therapeutics have been under clinical investigation for more than 30 years[3] for several diseases [4].
Considering the anatomical architecture of bladder, the therapeutic principle for intravesical instillation of ODN is very appealing as it provides ease of local administration with restricted systemic side effects due to limited serum uptake of antisense ODN. However, applied research for bladder diseases has lagged behind other disciplines. Drug development of this approach has been hampered by inefficient cellular uptake of the ODN. Bladder uptake of naked ODN is generally poor, but is improved in presence of bladder cancer, when very high concentration of naked ODN [5] is instilled. It is known that tight junctions in urothelium are compromised in cancerous condition [6] and therefore the strategy of relying on concentration gradient may not work in non-cancerous diseased condition where the barrier is intact, such as in overactive bladder.
Several approaches have been tried to increase the bladder uptake of ODN without compromising the bladder barrier, but all have limitations. Cationic lipids have been used in the past to deliver ODN [7, 8], but that method requires organic solvents and expert handling for formulating the ODN and lipid together prior to use. The binding between the negatively charged DNA phosphate groups and the cationic lipid [8] or peptide carrier is achieved by ionic interaction. Traditional approaches using cationic peptides or polysaccharides [9] require covalent binding between the vector and the drug. Covalent binding to cationic peptide polylysine requires elaborate application of chemistry tools [10, 11].
The translation of basic antisense research into therapeutics is also impeded by intracellular stability of ODN and potential for “off-target” gene silencing, immunostimulation, and other side effects. Phosphorothioate-modified ODN[12] are lipophilic and have increased stability against nucleolytic degradation [13].
A significant limitation for medicine, particularly treatments given by the intravesical route (via a catheter into the bladder), is the poor permeability of the bladder to outside agents. Efficient cellular uptake of many chemical agents is still a challenge.